[R-pkg-devel] active bindings in package namespace

[Jack O. Wasey]

Dear all,

I am developing a package which is a front for various online data 
(icd.data https://github.com/jackwasey/icd.data/ ). The current CRAN 
version just has lazy-loaded data, but now the package encompasses far 
more current and historic ICD codes from different countries, these 
can't be included in the CRAN package even with maximal compression.

Other authors have solved this using functions to get the data, with or 
without a local cache of the retrieved data. No CRAN or other packages I 
have found after extensive searching use the attractive active binding 
feature of R.

The goal is simple: for the user to refer to the data by its symbol, 
e.g., 'icd10fr2019', or 'icd.data::icd10fr2019', and it will be 
downloaded and parsed transparently (if the user has already granted 
permission, or after prompt if they haven't).

The bindings are set using commands alongside the function definitions 
in R/*.R .E.g.

makeActiveBinding("icd10cm_latest", .icd10cm_latest_binding, environment())
lockBinding("icd10cm_latest", environment())

For non-interactive use, CI and CRAN tests, no data should be 
downloaded, and no cache directory set up without user consent. For 
interactive use, I ask permission to create a local data cache before 
downloading data.

This works fine... until R CMD check. The following steps seems to 'get' 
or 'source' everything from the package namespace, which results in 
triggering the active bindings, and this fails if I am unable to get 
consent to download data, and want to 'stop' on this error condition.
  - checking dependencies in R code
  - checking S3 generic/method consistency
  - checking foreign function calls
  - checking R code for possible problems

Debugging CI-specific binding bugs is a nightmare because these occur in 
different R sessions initiated by R CMD check.

There may be legitimate reasons to evaluate everything in the namespace, 
but I've no idea what they are. Incidentally, Rstudio also does 'mget' 
on the whole package namespace and triggers bindings during 
autocomplete. https://github.com/rstudio/rstudio/issues/4414

Is this something I should raise as an issue with R? Or does anyone have 
any idea of a sensible approach to this. Currently I have a set of 
workarounds, but this complicates the code, and has taken an awful lot 
of time. Does anyone know of any CRAN package which has active bindings 
in the package namespace?

Any ideas appreciated.

Jack Wasey